Dip forming tubing



Inventor- /Qobez- M )Cdr-ke b Mw United States Patent ce 3,094,752Patented June 25, 1963 3,094,752 DIP FORMING yTUBING YRobert M. Parke,Schenectady, N.Y., assignor to General kElectric Company, a corporationof New York 'FiledDem 1, `1960,'Ser."No. 73,069 .'1`Claim. (Cl. 22-203)This'inventionrelates to dip forming tubing `and more `particularly toan improved method lof dip forming a tubing about a central'core withsubsequent removal of the core.

Variousmethoda'such vaswelding, casting or extruding,'are utilized inpresent manufacturing practices, generally'depending on themetalinvolved, to provide metallic tubing. -In themanufacture of tubingfrom the harder metals, such as, iron and steel, the metal maybeprovided in the form of a sheet or ystrip which is rolled andcontinually welded in order to form a tube. Alternatively, tubes fromsuch metals maybe cast-by welllknown casting processes. 'Of the-softermetals, such as, aluminum, copper, lead, tin, etc., tubesmay-be formedby anextrusion process. Thislatter process may provide -tubes of 25 toSO-'feet in length and greater. "However, -thehardermetals are quitedifcult to extrude, the prac- Vticalitiesand-economicsof manufacture arevery high,

and thus resort is-made to casting and welding. Those metals which areeasily extrudible, the softer metals, are often limited'inlength becauseYthe apparatus employed must'generally be aslong as theeifective lengthsof the tubing. "There are alsopractical and economic problems inbothprocesses -because of the necessity of starting with a solidpreformed body. In either process, it is understood,fzthat in orderto'providea separate interior ilining, yfor example, Va noncorrosiveone, separate -or additional means is necessary, if feasible. It is thusvery desir-able tohave an economical and practical process ftoprovidetubing of short or long lengths from various metals, both theharder and softer metals and without the necessity of Vstartingwithpreformed bodies and at the-Sametime providing alining therefor ifdesirable. `It

hasbeen discovered that the inherentproblems and diiculties as describedmay be overcome bythe application v,of la dip forming process in tubemanufacture.

Accordingly, itzis an object of this invention to provide Yan improvedmethod of producing tubing.

-It isanother object-ofthis invention to provide an improved method ofdip forming tubing.

iIt is still..another object ofthis invention to provide animprovedmethodof .dip forming.' tubing of extensive lengths.

It is another object ofv'this yinventionto provide an -improved methodof dip forming .tubing with coated interiors.

Briefly described, this invention includes passing .a wire, core or rodof a low-temperature1melting point material ythrough a bath of a'hightemperature melting -pointfmaterial and regulating therate oftraversal of the corethrough the molten bath -so that the high temetc.

Lbaths, etc. :wire 1 in ya solidstatehaving a rst cross sectional con-`guration and area iswcontinuously withdrawnfrom a Vsteel solidies onthe-strip-and'the'stripis -therefore increased in size,or,-thatonemetal, for example-iron, may be passed through a bath ofadissimilarmetal, for eX- ample, Zinc, to have a zinc-coating solidifiedfthereon. 'Similarvprocesses maybe employed either for joining purposesas in tube manufacture or for increased wall section, However, `theseVprocesses relate -to .what may be described as a single occurrenceprocess which provides ya -given coating to agiven structure with theadded coating remaining as an integral structure with the vcoretoproduce a final product. `given to ythe-dip 'forniing process intubingmanufacture .primarily because of appreciably Vdiminishing theecolnomicfactor. vAs beforestated,it is extremely difficult `to extrude,for example, harder metals as ziron, steel,

SeriousA consideration has L been nickel,retc.in:tube formand it is.a1sodiicultltoprovvide extensive lengths of tubings from these and othersuch metals.

Accordingly,.it hastbeendiscovered that metal tubings,

also of the hardenmetals, and of extensive lengths 'may be-providedbymeans of an unique application'ofthe dip forming process. .Essentially"thisiprocess includes passing ametal wire, rod orcore, forexample,silver,'through .a bath of, for example, iron, to provide a solidifiediron coating'or'tube onthe silver .core'bydip formingprocess.Thereafter, thcscomposite structure is heated yjust above themeltingzpointof the silver 4so thatithe silver isliqueed and removedfromthe Vcomposite structuretozprovide an iron tube. A.dipformingpprocessand apparatus ,is the Asubject of. a copending"applicationfS.N. 530,283,Carreker, `filed...n1gust Z4, `19:55, `now U;S. .Patent.No. 3,008,201,

and `assigned :to 'the Vsame .assignee as ',the present invention. Thefsubject of this `copending applicationis :included 4by referenceVherewith and ,'the apparatus r`used .thereinis ,apreferred form of the.apparatus and insofar 'as applicable, the stepwiseprocess to beemployed'in-the practice :ofthis invention. Accordingly, :FIG. 1 -ofthis application, is similar to FIG. lof'the aforementioned 'copendingapplication.

4Referring now to FIG. 1, there is villustrated aschematicrepresentation tof a dip Vforming apparatus ofths invention as oneworking example. Exemplary materials to becdescribedfin yrelation-.tooneworkingexample are iron J*and silver, although -t is to-be understoodthat various othercombinations, such as, cOPper-SteeLand othersto 'behereinafter described maybe suitably employed. Silver thas 'a meltingpoint-otabout 960 C. --and is readily 4available or easily .produced inwireor'rod form, but more particularly, `represents lno difficu'LtYproblem in zextrusion'ibecausegofits :good ductile properties.Furthermore, silver may be `readily '.and` easily cleaned. by -wellknown chemical cleaning compositions, .such as acid As illustrated inFIG. 1,'an elongated silver -storage means 2, such as, a reel orthelike, and isgguided by Vany appropriatefmeans, such as, asheath,;pulleyror drum 3 through .preliminary treatment appanatusA. Ap--paratus 41in .this instance includes'i-a-well known roll type ofYstraightening `dev-ice ,for the silver wire 1. After -t-raversingi-the:straightener-4, the wire '21 yproceeds-into a conventionalsurfacecleaningwapparatus y5, for example, .an '.electrolytic cleaningbath, and arinsing or washing bath 6. The-straightened, cleanandwet-wire 1 is then guided by guide means 7, which is sirnilar to-guide means 3, intoiand through an elongated enclosure orwtubularconduitl 8. Conduit S'includes Aa drying means 9, whichLmay besuppliedwitha Ineutral atmosphere'from asource 10,

`ancil conventional power drivenfeed rolls 11 which fricytionally engageand drive wire 1 intoa'vacuum Ventrance chamber 12. `Chamber '12.isprovided with a vacuum source 13 which permits the wire to pass intochamber 12, but prevents the passage of atmosphere therewith. Wire 1then proceeds into an entrance port 14 provided in the bottom of acrucible 15, and then passes through a bath of molten material, forexample, iron, which is contained in Crucible 15. The molten iron incrucible 1S accretes or ldeposits and solidiies upon and around theouter surface of si-lver wire 1 as a sheath or coating, increasing itscross sectional area appreciably, and provid- .ing :an elongated andcomposite body 16 as best shown in FIG. 2.

Referring now to FIG. 2, wire 1 is illustrated as passing throughyentrance port 14 and through the molten bath of iron 17. Molten iron 17commences solidifying on Wire 1 adjacent the entrance port and continuesto attach or solidify on wire 1 in increasing quantity until wire 1 haspassed through the bath. The r-ate of deposition is of course dependenton the kind of metals employed -together with their related meltingpoints and more impor-tantly on the rate of traversal of the Wire 1through the bath. Since dip forming, to apply steel on steel, lead oncopper, tin on copper and zinc on steel, etc., is Well known, thevarious design conditions for the practice of this invention are easilycalculated or set up. Ordinarily, the requirements are that the metalshave sulliciently different melting points commensurate with transittime in the bath, 4or rate of traversal therethrough, such that meltingof the core material is substantially prevented. The temperaturedifferential is not, however, the prime requisite. It is further denedby saying that the heat capacity of the core material must besutiiciently high so that the core material may take up or adsorbsuicient heat from the bath material to provide solidica-tion of thebath material Without melting of the core material. In a working exampleof this invention, a silver wire of about 1 inch yto ll/z inches indiameter, at room temperature, may be fed through a molten bath of ironor steel at about 1570o C. With la rate of travel of about 25 to 300feet per second or about a l second transit time, a l/l to 1/8 inchcoating is attained. A further working embodiment of this inventionapplies to the formation of copper tubing utilizing lead or tin as thewire or core material. Best results lare obtained when the core materialhas been precleaned as described and where vacuum entry is employed.

After emerging from cruoible 15, the silver-iron composite body ispassed into a sizing apparatus, such as, a pair of sizing rolls 18.Apparatus 18 functions to remove or correct minor surface irregularitiesand provide the proper or predetermined O.D. In this respect, it is tobe understood that shrinkage or contraction of the coating about thecore material or wire introduces stresses in the coating which may leadto cracking. Such cracking is dependent on the various metalcombinations employed, time-temperature conditions and the Sizes or wallthicknesses of the final tube. These conditions may be prevented orminimized in marginal lapplications by providingA surface variations inthe core material so that contraction of the coating may be adsorbed bymovement of the oore material. Alternatively, the core material may beporous or hollow, etc. It is to be noted that a splined or corrugatedcore configuration may be employed to provide a resultant tubularconfiguration having internal projections or ns. Composite body 16 isguided by means of a temperature controlled duct conveyor 19, to anysuitable receiving means, such as a reel 20, where it may be temporarilypermitted to accumulate. Thereafter, the composite body 16 is Withdrawnfrom receiving means 20 and passed through winding and cutting apparatus21 whereby body 16 is suitably wound, or cut to length, `and manually orautomatically placed within a furnace 22 in order that the temperaturemay be raised suiliciently to melt the silver and the silver removedtherefrom. Furnace 22 may be suitably combined lwith the same furnaceutilized to melt the iron in crucible 1S.

The resulting :iron tube is removed as the final product as indicated byarrow 23. K

From the foregoing, it may be readily understood that an apparatus isprovided in which continuous casting or dip forming by accretion upon alength of core material provides an increased cross sectional materialwhich may thereafter be processed into tubular form. One or more passesthrough bath 15 may be made depending on the final tube size desired.The composite body 16 also may be arranged in various configurations infurnace 22 to have molten silver ow therefrom by gravity, such as by'having the composite body wound into a configuration similar to anArchimedes screw, or it may be rotated, or suitably moved to provide thesame result. A connection is illustrated between furnace 22 and storagemeans 2 to indicate that the silver may be solidied and extruded in wirefor-m for a repeat of the process, or to indicate closed circuitry wheredesired.

TWo important advantages are to be gained 4by the practices of thisinvention. One of these important advantages is the production of tubesin an etiicient and economic manner vof those metals difficult toextrude and also a more economical production of ordinary tubing, suchas for example, copper and the softer metals. In addition to the generalpractices of this invention, nonmetals also may be employed as a corematerial together with other metals or non-metals. A unique example isthe utilization of mercury in the frozen state to provide tubularoonguration from metals or non-metals from which the mercury may beextracted at room temperature. In any instance, best results areobtained when the melting points of the materials are reasonably spacedwith consideration of the heat capacity of the core material to avoidmelting of the core material. A difference of about 300 C. is preferredfor most metals.

The second important advantage in the process is the provision of acoating or lining in tubular configuration. In many industrial processesand in particular in food processing apparatus, there is required, ordesired, extensive lengths of relatively low cost tubing having apreferred internal coating which is generally non-corrosive or whichdoes not affect taste of the products ilowing therethrough. Thesilver-iron combination provides a thin silver coating in an iron tube,and in the tin-copper combination, the process provides a tin coating ona copper tube. The coating or alloyng, referred to as joining, iscontrolled first by the choice of materials used, i.e., where thematerials are or are not capable of alloying with each other, and towhat degree. The thickness of the lining or the extent of alloying may:be controlled by controlling the rate of cooling of the compositestructure 16 in temperature duct 19 after it leaves bath 15, with longercooling periods providing increased thickness of coating or increasedalloying.

-In extensive operation a furnace 22 may be provided to replenish moltenmaterial in crucible 15 in order to maintain a predetermined level anduniform size of the composite body. Starting of the sequence isfacilitated, for example, by employing a starting section of the corematerial of a material having a higher melting point than the bathmaterial, or by suitable apparatus which will commence drawing wire 1through Crucible 15 at the entrance seal 14, or by a tlying startprocess. The rod wire or core material of this invention may be an alloyas well as the bath material may be an alloy. Core alloys may bedesirable for various purposes, for example, for increased strength suchas, a copper lead alloy as a core material where lead alone would be toosoft.

While a specic method and apparatus in accordance with this inventionhas been shown and described, it is not desired that the invention belimited to the particular description nor to the particularconfigurations illustrated, and it is intended by the appended claim tocover all modifications within the spirit and scope of this invention.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

An improved method of forming tubular congurations of a given metal withan integral metal lining therein which comprises providing a moltenmetal bath of iron, providing -an elongated core of a solid state metaltaken from the class consisting of copper, silver, tin, aluminum, leadand nickel, passing the said core through the said bath in -a dipforming process to provide a coating of iron on said core to form acomposite body, thereafter passing said composite body through atemperature controlled duct, controlling the rate of cooling of saidcomposite body in said duct to in turn vary the coating action betweensaid iron and said core providing a lining for said iron, and thereafterheating said composite body for melting and removal of the remainder ofsaid core resulting in an iron tube with a core metal lining.

References Cited in the file of this patent UNITED STATES PATENTSFOREIGN PATENTS Great Britain July 22,

